1. Field of the Invention
The present invention relates to a transmission device and a label allocation method for allocating a label having a predetermined relation between a main route and a protection route based on an autonomous operation.
2. Description of the Related Art
In recent years, a multi-protocol label switching (MPLS) as a route control protocol of a label switching and a signaling protocol are becoming popular. According to the label switching, an identification code called a label is attached to a frame (a packet), and a route is controlled using this label. The label needs to be allocated to each path in advance. In a large scale network, load of allocating the labels by an administrator increases.
When the signaling protocol is used, a node (a transmission device) such as a router and a switch that constitute the network, autonomously allocate the labels to the paths, thereby substantially decreasing the load on the administrator. Because paths can be established without requiring manpower, additionally required paths can be established promptly. As a representative signaling protocol, there is a Resource Reservation Protocol-Traffic Extension (RSVP-TE) prescribed in D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, G. Swallow, “RSVP-Te: Extensions to RSVP for LSP Tunnels”, [online], December 2001, retrieved from the Internet (hereinafter, “Reference 1”).
FIG. 32 is a diagram to explain an outline of label allocation-based on signaling. As shown in FIG. 32, the allocation of labels based on signaling is achieved by exchanging a connection establishment request message (Path message, hereinafter, “PathMsg”) and a connection establishment response message (Resv message, hereinafter, “ResvMsg”) between an ingress node as a starting point and an egress node as a terminal end.
PathMsg is a message for requesting the establishment of a path, and includes route information known as explicit route object (ERO), requested band information, and the like. ResvMsg is a message for notifying a label allocated by a downstream node to an upstream node.
A process of the signaling is as follows. The ingress transmits a PathMsg, which includes the ERO as a route till the egress, and the requested band information, to an adjacent node. The PathMsg transmitted by the ingress is transferred to the egress based on the ERO.
When the PathMsg reaches the egress, the egress establishes a path between the adjacent upstream node to meet the requirement of the PathMsg, and notifies an allocated label to the upstream node using a ResvMsg. The establishment of a path and the notification of a label using the ResvMsg are carried out sequentially in the upstream direction. When the ResvMsg reaches the ingress, the entire path is established, and all the labels are determined, therefore communication can be carried out using this path.
Usually, labels allocated to the nodes have different values. However, these labels can be standardized. To standardize the labels, a function of limiting a label is used. FIG. 33 is a diagram to explain label allocation using a label limit function. When the label limit function is used, a PathMsg transmitted includes a label set within the message. The label set is information indicating that a label is to be selected from a range of labels. Each time when the PathMsg is transferred, a label that is already used in the node is excluded, thereby narrowing the selection range.
In the example shown in FIG. 33, the ingress assigns 1-16 as a label set. This value is narrowed each time when the PathMsg is transferred. When the PathMsg reaches the egress, this value becomes 8-10. This value indicates that labels within this range are not used by any of the nodes between the ingress and the egress.
The egress allocates a label from this range, and notifies the allocated label to the adjacent upstream node using the ResvMsg. The upstream node allocates the same label as that notified from the downstream node, and notifies the label to the next upstream node. In this way, the label of the common value is allocated to all the nodes between the ingress and the egress.
MPLS is extended to Generalized Multi-Protocol Label Switching (GMPLS), and the GMPLS is applied to a ring network using an optical fiber such as a Synchronous Optical Network (SONET), in which extension of the function of the RSVP-TE is considered. The SONET and the like have a redundant mechanism called a ring protection. The main purpose of the extension is to effectively use this redundant mechanism. For details, see: Louis Berger, Igor Bryskin, Dimitri Papadimitriou, Adrian Farrel, “GMPLS Based Segment Recovery”, [online], October 2004, retrieved from the Internet (hereinafter, “Reference 2”).
However, even when the extended RSVP-TE function is used, sometimes this cannot sufficiently support the redundant mechanism such as the SONET. When communication is carried out over a SONET ring of a multi-ring configuration, generally, a protection route is set in addition to the main route. In this case, in order to automatically switch for the main route to the protection route at the time of trouble, a predetermined relation needs to be established between a channel (labels) for the main route and a channel (labels) for the protection route.
When the extended RSVP-TE function is used, labels can be allocated to the main route and the protection route in one signaling, but a relation cannot be established between the two routes. Instead of using the signaling, an administrator can manually set a route. However, in a large scale network, the load on the administrator increases, and a new path cannot be established promptly.